Anti-collision light for aircraft

ABSTRACT

Anticollision-lamp operable in day-light and at night. It is known to provide separate day-light lamps with a high light output, and night-lamps with little infrared radiation in order not to dazzle night vision goggles. The anticollision light according to the invention comprizes at least one optical interference filter ( 11 ) with an average transmission factor in the infrared which is less than 4% of its value in the visible white or red. Preferred embodiments comprize among others: an average transmission factor in a spectral domain larger than 80%, preferably 90% and most desirably 95%; the combination of an interference filter ( 11 ) with an absorption filter ( 10 ) transparent for red light; an interference filter ( 11 ) consisting of several plane elements arranged octagonally; and a band-pass interference filter with a transmission domain situated in the visible red and the transmission factor of which is at least 10 4  times larger than in an infrared domain.

RELATED APPLICATIONS

This application claims the priority of the European patent applicationno. 01 114 424.3, filed on the 15^(th) of Jun. 2001, the whole contentof which is hereby included by reference.

TECHNICAL FIELD

The invention relates to an anticollision light for aircrafts.

STATE OF THE ART

The international regulations for airborne aircrafts (e.g. “JAR”=JointAviation Regulations, “FAR”=Federal Aviation Regulations) with fixedwings or rotary wings require an external lighting which in addition tothe position lights requires so called anticollision lights which mustradiate by day and by night above a certain minimal intensity indicatedin Candela. According to JAR 23/25/27/29 the anticollision lights muste.g. radiate in red (“aviation red”) or in white (“aviation white”) witha predetermined intensity and colour, and also within a given solidangle.

An usual source for flashing anticollision lights is e.g. provided byXenon flashing tubes which emit a light spectrum that appears white tothe human eye, and which is provided with a red filter (typically a redglass) for operation in the red spectral region.

This leads to the following problem due to the ever increasing use ofnight vision goggles (so called NVG), in particular by militaryaircrafts. The anticollision light (ACL) of anticollison lamps accordingto JAR/FAR 23/25 and 27/29 also generates an infrared radiation whichoverloads night vision goggles of all types and therefore dazzles theirusers. If one wishes to make an aircraft operational both under JAR/FARregulations and NVG regulations then it is necessary to provide onaircrafts which are equipped for NVG operations, in addition to otherlight sources, anticollision lights which satisfy the NVG specifications(e.g. according to MIL-L-85762A). This is achieved either throughappropriate modifications, or the lighting system must be provided withadditional so-called NVG-lights which are NVG compatible. Theanticollison light which is in use day and night is a strong lamp theintensive infrared radiation of which raises no problems because nonight vision goggles are used during daylight; contraryvise the NVG lampeither radiates with a lesser intensity and/or it carries an opticallyquite dense coloured filter which also strongly reduces the radiation inthe infrared domain. In this way the disturbance of night vision gogglescould until now be lessened or avoided whilst at the same time thesensitivity of the human eye, which is much higher in darkness, enabledthe radiation which this system admits in the visible spectral domain tobe fully sufficient for avoiding collisions. However, this solution hasdrawbacks, such as the high costs of the necessary modification, therequirement for expensive additional components, and also the additionalweight.

DESCRIPTION OF THE INVENTION

In order to avoid these drawbacks the invention is defined as recited inthe main claim.

The solution according to the invention consists in an anticollisionlamp for aircrafts which comprises at least one optical filter, theaverage optical transmission factor of which in a first spectral domainis smaller than 4% of its value in a second spectral domain, where thefirst domain lies on the longwave side and the second domain lies on theshortwave side of a transition interval situated between the visible redand a boundary located in the infrared region. The low transmission inthe infrared makes a disturbance of night vision goggles impossible. Atthe same time the high transmission in the white or red spectral domainallow it, to satisfy the requirements for a minimal visible lightintensity in day-light and for a maximal allowable infrared lightintensity at night with one and the same anticollision lamp, and itallows in particular to operate the lamp at the same power. Thedependent claims describe preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further implementations, advantages and applications of the inventioncan be derived from the dependent claims and from the followingdescription made with the help of the drawings. Therein,

FIG. 1 shows a simplified perspective view of an embodiment of theinvention;

FIG. 2 shows a schematic axial section through the embodiment of FIG. 1;

FIG. 3 shows a very schematic section along III-III of FIG. 2;

FIG. 4 shows an instance of a transmission diagram of the infraredfilter of the embodiment according to FIG. 1; and

FIG. 5 shows an example of further a preferred transmission diagram ofthe infrared filter.

PREFERRED EMBODIMENT OF THE INVENTION

FIG. 2 shows a much simplified a vertical axial section through theembodiment of the invention shown in perspective view in FIG. 1. Thelamp is attached through a bolt 2 on a base 1 and it comprises a baseplate 3 and a cover plate 4; a Xenon flashing tube 6 of a readilyavailable type is fixed between both plates. In order to obtain anessentially circular emission in all directions, the Xenon flashing tube6 can e.g. essentially have the shape of a ring or a torus. The base ofthe tube, which lies outside the plane of the drawing and which deviatesfrom the torus-like shape, is mechanically attached in the usual way(not shown) within the housing of the lamp, and it is electricallyconnected to electrical conductors (also not shown) which lead to asocket 5 attached on the base 1. The socket comprises contacts for thecurrent needed by the Xenon tube 6 and also for igniting the flashes inthe tube. The socket is physically shaped so as to fit into acorresponding fitting provided on the outside of the aircraft, so thatit can be connected in the usual way to this fitting. A two-partreflector 7, 7′ surrounds the torus-shaped part of the Xenon cube 6 andis itself essentially shaped like a torus split along its outerperiphery. The cups of the reflector extend at least across about 200°,and preferably across 360°, a place for the socket of the Xenon tube 6being provided in one cup 7. Preferably, the cups 7, 7′ of the reflectorare shaped so as to optimally direct the radiation issued from the tube6 into the desired solid angle and also distribute the radiationthroughout this angle. To obtain this the section of the cups can be anarc of circle as shown in FIG. 2, but if the distribution of the lightrequires it, they can also be shaped differently, e.g. as parts of conicsections. In order to obtain a good efficiency within the desired solidangle the vertical aperture α seen in the section will be less than180°, preferably less than 130° and most desirably smaller than 90°. Thereflector cups 7, 7′ are fixed within the lamp casing in anymechanically appropriate way, e.g. with the help of shims surroundingthe bolt 2, of which only shim 8 is sketched in the drawing, and throughadequate threads (also not shown) which are arranged so that the upperreflector cup 7′ can easily be removed when it becomes necessary toreplace a spent tube 6.

A cup-shaped glass filter 10 encloses the reflector 7, 7′ in order tofilter out the wave lengths below the visible red, which aims at makingthe light look red; the action of this filter on wave lengths in theinfrared domain, i.e. above about 680 nm, is irrelevant, however. Thereis no filter 10 for a white anticollision lamp. The filter 10 issurrounded by a further filter 11 which filters out wave lengths abovethe visible red domain, so as not to disturb night vision goggles. Inthe present example the filter 11 comprises 8 octogonally arranged glasspanes 11, as best shown in FIG. 1. The panes 11 form a filter 11, e.g.by way of layers which are vaporised in a known fashion on its inner,protected surface; this provides an interference filter which to a largeextent removes radiations in the infrared domain, i.e. from about 680 nmup to at least 850 nm, and preferably up to 1000 nm, e.g. as shown bythe diagram of FIG. 4. This avoids a disturbance or the overload ofnight vision goggles which work in the infrared, independently of theeffect, and in particular the transmission, of the inner filter 10 inthe infrared domain, and also independently of the intensity of the tube6.

Further embodiments are defined in the dependent claims, such as: anaverage transmission factor in the first spectral domain which issmaller than 1%, preferably smaller than 0.4%, and most desirablysmaller than 0.1% of its value in the second spectral domain; an averagetransmission factor in the second spectral domain which is larger than80%, preferably larger as 90%, and most desirably larger than 95%; afirst spectral domain which extends into the infrared as far as 850 nm,and preferably at least as far as 1000 nm; a second spectral domainwhich extends at least across a spectral domain which appears white, inparticular across at least the entire visible spectrum (whiteanticollision lamp) or at least over a visible red spectral domain (redanticollision lamp); a boundary between the first and the secondspectral domain which lies between 640 nm and 700 nm, and preferablybetween 660 nm and 680 nm.

FIG. 3 shows a very schematic section along a line III-III of FIG. 2, inorder to clearly illustrate the relative positions of filter 10 and 11,and of the active part of the Xenon tube 6 which has the shape of anincomplete torus. The segmentation of the interference filter 11 intoeight plane elements is a practical measure taking into account the factthat there are certain difficulties in vaporising interference layersonto a curved surface. If these difficulties are irrelevant, the filter11 can equally well consist of one or several cylindrically curvedsurfaces. The octagonal disposition of the flat interference surfaces 11of the filter, or alternatively a curvature of the filter surface 11,serve to realize an anticollision lamp able to radiate over a largeangular domain, and preferably essentially in all direction, i.e. acrossabout 360°.

The filter 11 will preferably have a transmission curve which isidentical or similar to that shown in FIG. 5, i.e. which has anessentially vanishing transmission factor above a boundary that lies inthe interval between 600 nm and 700 nm. For a light falling orthogonallyon the filter this transmission factor will preferably be below 2⁻⁷, andit diminishes at least by a factor 10⁴ between 600 nm and 700 nm. Thisand the arrangement of the filter outside of filter 10 which isessentially transparent in the red domain, makes it possible to avoidwith little expenditure the dazzling or overload of night visiongoggles, even when using strong light sources. This preferred filtercharacteristic thus has a high transmission rate in the desired domain,and a steep flank. The value for the NVIS radiance is very small and ispreferably NRb <2⁻⁷ at 0.1 fL.

This anticollision lamp can be used for aircrafts of all types but ismainly intended for helicopters and airplanes.

1. Anticollision light for aircrafts characterized in that it comprisesat least one optical filter (11) the average optical transmission factorof which in a first spectral domain is below 4% of its value in a secondspectral domain, where the first domain lies on the longwave side andthe second domain lies on the shortwave side of a transition intervalsituated between the visible red and a boundary located in the infraredregion.
 2. Anticollision light for aircrafts according to claim 1,characterized in that the average transmission factor in the firstspectral domain is below 1%, preferably below 0.4%, and most desirablybelow 0.1% of its value in the second spectral domain.
 3. Anticollisionlight for aircrafts according to claim 1, characterized in that theaverage transmission factor in the second spectral domain exceeds 80%,preferably 90%, and most desirably 95%.
 4. Anticollision light foraircrafts according to claim 1, characterized in that the averagetransmission factor in the first spectral domain is less than 2−⁷ andthat it sinks at least by a factor of 10⁴ between 600 nm and 700 nm. 5.Anticollision light for aircrafts according to claim 1, characterized inthat the boundary lies between 640 nm and 700 nm, and preferably between660 nm and 680 nm.
 6. Anticollision light for aircrafts according toclaim 1, characterized in that the first domain extends at least up to850 nm, and preferably as far as 1000 nm into the infrared. 7.Anticollision light for aircrafts according to claim 1, characterized inthat the second spectral domain extends at least over a visible whitespectral domain, or at least over a visible red spectral domain. 8.Anticollision light for aircrafts according to claim 1, characterized inthat it comprises a further filter (10) which attenuates wave lengthsbelow the visible red light.
 9. Anticollision light for aircraftsaccording to claim 8, characterized in that the further filter (10) isplaced between the light source (6) of the anticollison light and the atleast one optical filter (11).
 10. Anticollision light for aircraftsaccording to claim 1, characterized in that the one filter (11) is aninterference filter (11), and in particular that the further filter (10)is an absorption filter (10).
 11. Anticollision light for aircraftsaccording to claim 10, characterized in that the interference filter(11) consists of several flat elements (11).
 12. Anticollision light foraircrafts according to claim 1, characterized in that the one filter(11) is an interference band-pass filter with transmission band situatedin the region of visible red light.
 13. Anticollision light foraircrafts according to claim 10, characterized in that the band-passfilter consists of several flat elements.
 14. Anticollision light foraircrafts according to claim 1, characterized in that it comprizes aflashing light source (6) in the shape of a fluorescent tube which windstorus-like over more than 200° around an axis (2), and is surrounded bya reflector (7, 7 ¹) which also extends in an essentially torus-likeshape over more than 200° and exhibits a slit along its outer periphery,where the aperture of the slit, as seen from the circular longitudinalaxis of the fluorescent tube (6) in a plane containing the axis, has amaximal aperture angle (α) of 180°, preferably of 130°, and mostdesirably of 90°.